Variable Speed Drives

A variable speed drive is a drive that controls the speed and rotational force of a motor and is capable of changing the speed of the drive steplessly from zero to full. Variable speed drives are used primarily for process control, but increasingly for energy conservation benefits as well. The term variable speed drive is sometimes used interchangeably with the term adjustable speed drive, though at times they also have slightly different meanings (see below).

Variable Speed Drive Manufacturers

  • Zero-Max has been providing servo motion control solutions for over 60 years and is a manufacturer of variable speed drives, shaft couplings, and keyless lock bushings. Zero-Max has strategic distribution points throughout the globe to deliver motion control solutions to customers world wide. Zero-Max was founded when Sterling Stageberg invented a unique mechanical variable speed transmission drive, and has led the motion control industry ever since.

Adjustable vs Variable Speed Drives

The terms adjustable speed drive and variable speed drive are sometimes used interchangeably, and sometimes used to refer to slightly different drive characteristics.

In common parlance, an adjustable speed drive refers to a drive in which the speed can be adjusted in certain predetermined stops. Thus a typical oscillating fan is an excellent example of an adjustable speed drive: it has a low, medium, and high setting, but you cannot select a drive speed in between low and medium.

A variable speed drive typically refers to a drive that is infinitely adjustable from zero up to the maximum drive speed. Any drive speed can be set, and the drive speed can be continuously and minutely adjusted.

Variable speed drives are commonly used in servo and robotic applications, which require precise and constantly changing drive speeds. Variable speed drives are also used in a wide range of process control applications, and can be electronic or hydraulic in addition to a mechanical drive.

Variable Speed Drive Uses in Process Control

The variable speed drive was developed for its many uses in process control. Variable speed drives can result in smoother operation, give vital control over acceleration speeds, allow adjustments in operation speed depending on workflow, and control the torque or tension in a drive.

The primary purpose of the variable speed drive is to control the speed, torque, directional rotation, and acceleration or deceleration of a motor. Some applications of variable speed drives include:

  • Irrigation pumps
  • Sewage pumps
  • Ski lifts
  • Fans for power plants
  • Ventilation systems
  • Milking machines
  • Robotic servos
  • Automation technology

For many processes a variable speed drive is necessary to allow the functionality of the process, but many other processes can function without a variable speed drive, but obtain significant energy efficiencies when variable speed drive technology is implemented.

Variable Speed Drives and Energy Conservation

While variable speed drives and adjustable speed drives were originally developed for specific process control applications, their use is more and more common as a method of energy conservation.

The most common energy conservation applications of variable speed drives are in pumps and fans. Fans or pumps making use of a static speed drive often provide more airflow or liquid flow than is necessary for the application. This airflow or waterflow is often regulated via a damper designed to restrict the flow.

However a variable speed drive in the same application allows for more precise regulation of the airflow or waterflow without the need for the damper by lowering the speed of the fan or pump when needed, while still retaining the ability to achieve the higher operating speed. A reduction in the speed of a fan or pump correlates to a reduction in power consumption, which is both environmentally friendly and reduces energy costs.

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